Loud speaker



June 20, 1933. P. cRosLEY, JR

LOUD SPEAKER Filed Oct. 17, 1929 INVENTOR.

A TTORNEKS Patented June 20, 1933 UNITED STATES PATENT orr ce POWEL CROSLEY, .13., OF CINCINNATI, OHIO, ASSIGNOR TO THE. CROSLEY RADIO CORPORATION, OF CINCINNATI, OHIO, A CORPORATION OF OHIO LOUD SPEAKER Application filed October 17, 1929. Serial No. 400,396.

My invention has to do with loud speakers utilizing a cone as a diaphragm or tympanum, and its particular object is the. provision of a new type of support for diaphragms in loud speakers.

The motor of present day loud speakers is designed to be capable of producing vibrations corresponding to fluctuations in an electric-current, and the problem in connection with the reproduction of sound is to develop a diaphragm or. tympanum which may be connected to the moving coil of a loud speaker motor and which will radiate into the surrounding air sounds corresponding to the vibrations of the coil.

This problem is a difficult one; and due to the involved character of the equations for such a structure, any attempt at mathematical analysis becomes so cumbersome as to be practically impossible. Consequently, it has been found necessary in the development of loud speakers to conduct a long series of careful experiments in order to arrive at a form of diaphragm which would have the desired characteristics. Such efforts have necessarily been by way of trial and error.

Cones and members having conoidal surfaces have come into great favor as possessing, in a marked degree, the characteristics necessary for such a diaphragm or tympanum. The use of cones, however, introduces new problems which have to do first with the method of supporting the outside edge of the cones and second, where a moving coil type of motor is used, with the supporting of the middle of the cone in such a way as correctly to position the coil. The two problems are interrelated. It is practically impossible, with a cone of any size, to rely on a support at the apex to hold the coil in its proper position in the air gap of an iron cored electro-magnet. If the cone is not supported at its periphery, then the support ator near the apex of the cone has to be made considerably larger, with the result of blurring the reproduction of the cone. It is also desirable to protect the edge of the diaphragm against fluttering since, as is well understood, this produces extraneous noise in the material of the cone itself, and requires a damping of the vibrations ora' rigid structurefor the cone edge. 1 For these reasons it is advisable to provide a type of center support which shall be as small as practicable, and which will not in terfere with. the proper functioning of the cone, and in protecting the cone edge the large magnitude of movement which is imparted by the'moving coil calls for a rim or edge support for the cone which has a considerable latitude of movement.

A number of different methods of supporting the cone edge have been proposed and are now in commercial use. In general these comprise plane peripheral rim portions on the cone made of vibratile or partly vibratile material; both of which structures have several defects. The plane peripheral rim essentially dilfers in its sound-radiating characteristics from the cone itself because it has distinct resonances at particular frequencies in the audio range; and at these frequencies it produces a large amount of sound which distorts the quality of the sound produced by the cone proper, and the material used as a peripheral support must be stretched in order to serve the required locating function which tends to distort the sound from the conical portion of the diaphragm.

An object of my invention, therefore, is the provision of a type of support for a cone and coil which, While properly restraining the edge of the cone itself, will not enter into the production of sound and will leave the 5 cone free to vibrate with nothing more than the gentle restraining action of the edge support. p

Another object of my invention is the provision of a type of edge support for a cone 9() whichwill enable me to realize the best sound producing characteristics thereof. with the minimum of distortion; 7

These and other objects of my invention,

whichwill be pointed out hereinafter or will be apparent toone skilled in the art upon 7 reading these specifications, I accomplish by that certain construction and arrangement of parts of which I shall now describe a preferred embodiment, reference belng had to the drawing which accompanies these specifications.

In the drawing Figure 1 is a semi-diagrammatic sectional view through a loud speaker motor and dia phragm, showing my type of mounting.

Figure .2 is a front elevation thereof.

I have shown in the figures a cone 1 of vibratile material having attached thereto a moving coil 2 with a winding as is customary, mounted in proper operative relationship to the core of 3 of an electro-magnet. The coil is located in the air gap surrounding the central arm of the core. A post 4 is attached to this central arm and a center support 5 for the cone is provided and fastened at its center point to the post 4 by means of the screw 6. This support is of vibratile material, generally severed about its edge as at a 7, so that a portion of its periphery may lie on the surface of the cone as at 8. Staggered elongated slots 9 are formed in the support so as to increase its resilience and decrease its sound producing characteristics.

The outer ed e of the cone l is attached to an annular band or ring of felt 10 which, in turn, is clamped between a ring 11 and the annular rim portion 12 of frame member 13, by means of bolts l t. The frame member is attached rigidly to the iron core 3 of the loud speaker motor by screws 15.

The edge of the loud speaker diaphragm is preferably rolled or rounded or deflected as at 16, providing an outer portion 17, to which the felt ring 10 is articulately attached by stitching as at 18. Other configurations of the diaphragm edge are, however, successful, the important point being to impart some stiffness to the cone edge by the deflection of the material.

It is important that the felt ring be stitched rather than clamped, cemented or glued to the periphery of the diaphragm. If a clamp, glue or cement is used both the material of the diaphragm edge and the felt are stiffened by the clamp, glue or cement, and not articulated, and this hampers their freedom of relative movement and materially affects the performance of the structure.

The proportions and weights of the various parts must be appropriately chosen to secure the best results. In the particular form shown, I make the diameter of the base of the cone 7 while the diameter of the opening in the frame 13, or the inside diameter of the ring 11 is 8", so that between the diahragm edge and the clamping support there is a rim of supporting felt wide. Using a cone formed of starched and lacquered buekram, it is found that these proportions are very satisfactory and give an over-all performance throughout the range of audible frequencies superior to anything which has been obtained in the past with cones of these same dimensions otherwise supported. It is to be noted that in my structure the outer edge of the cone is actually supported rather than merely confined within a space and, for this reason, I am enabled to use a smaller central support 5, than would be possible with an unsupported cone edge. It will be further noted that resilience of support is provided for by the projection of the diaphragm material beyond the conical portion and the zone of sound deflection established by the bend in the cone material and that the felt which is a periodic is of very limited width and serves mainly as a linkage which is mechanically tight without the need of stretching and therefore acoustically free.

Various modifications may be made in my invention without departing from the spirit thereof.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

1. In a loud speaker comprising a diaphragm and a support around the outer edge part of the diaphragm, a ring of aperiodic material held by said support and articulately connected to said outer edge part of said diaphragm.

2. In a loud speaker comprising a diaphragm and a support around the outer edge part of the diaphragm, a ring of aperiodic material held by said support and secured to said outer edge part of said diaphragm solely by stitching.

3. In a loud speaker comprising a diaphragm and a support around the outer edge part of said diaphragm, a ring of aperiodic material held by said support and having its inner part in annular lapping contact with said outer edge part of said diaphragm and articulately secured to said edge part within the area of lapping contact.

4. In a loud speaker comprising a conical diaphragm with its outer edge part deflected into flat annular shape, and a support around said outer edge part, a relatively thick flat ring of aperiodic material held by said support and having its inner part in annular lapping contact with said flat annular edge part of said diaphragm and articulately secured to said edge part within the area of lapping contact.

5. In a loud speaker comprising a diaphragm and a support around the outer edge part of the diaphragm, a felt ring held by said support and held to said edge part solely by stitching.

POIVEL CROSLEY, JR. 

